Influence of the block copolypeptide surfactant structure on the size of polypeptide nanoparticles obtained by mini emulsion polymerisation

Polypetide nanoparticles obtained by miniemulsion polymerisation of amino acid N-carboxyanhydrides (NCA) are a novel class of tuneable bio-derived functional nano materials for potential applications in nutraceutics, agriculture, and medicine. This work discloses a facile route to stable hydrophobic polypeptide nanoparticles comprising a poly(l-phenylalanine) and poly(l-leucine) core, respectively, using two amphiphilic glycosylated block copolypeptide surfactants with hydrophobic poly(l-phenylalanine) or poly(l-leucine) blocks. All surfactant/core combinations produce stable nanoparticle dispersions with average particle sizes between 160 and 220 nm. However, analyses using light scattering techniques, SEM imaging and Asymmetric Field Flow Fractionation, reveal a particle size dependence on the surfactant/core combination in that particles are reproducibly 20-30% larger if the surfactant block is identical to the amino acid polymerised in the core. It is hypothesised that this is caused by complex hydrophobic and secondary structure interactions between the surfactant and particle core. These fundamental insights will inform the future design of polypeptide nanoparticle libraries utilizing many different amino acids for example in nanomedicine.